Optical disk device and optical disk recording and/or reproducing method

ABSTRACT

The present invention is applied to an optical disk apparatus which records data on and/or plays back data from one of a variety of DVD optical disks. The present invention generates a binarization threshold S 3  by offsetting an envelope S 2  of a playback signal RF by an offset voltage V 1 , and binarizes the playback signal RF (S 4 ) according to the binarization threshold.

TECHNICAL FIELD

[0001] The present invention relates to an optical disk apparatus and arecording method and/or a playback method of an optical disk, and isapplied to an optical disk apparatus that records data to and plays backdata from an optical disk complied with the DVD standards. In accordancewith the present invention, management information recorded in abar-code form is reliably played back from a variety of optical disks byoffsetting the envelope of a playback signal by an offset to generate abinarization threshold, and then binarizing the playback signalaccording to the binarization threshold.

BACKGROUND ART

[0002] Conventionally, management information is recorded in a bar-codeform on an inner track of a DVD optical disk, and is used to manage theoptical disk.

[0003] The management information includes information to inhibitcopying data, and identification information unique to the optical disk.As shown in FIG. 1(A), a high-power laser beam from a YAG laser isdirected to an inner track inside of the ordinary data recording area ofthe optical disk, thereby recording the management information bysuccessively evaporating a material on an information recording surfacein radial directions. In an ROM disk, the high-power laser beamevaporates a reflective aluminum film.

[0004] In a recordable disk, the high-power laser beam evaporates acolor film and a reflective film (of Au, Ag, etc.). In a rewritabledisk, the high-power laser beam evaporates a phase-change film and areflective film (of Au, Ag, etc.).

[0005] In DVD-ROM and DVD-RAM optical disks, the management informationis recorded on a BCA (Burst Cutting Area). The BCA is formed within arange of from 22.3(+0 and −0.8) through 23.5 (+0.1, −0.1) [mm] from thecenter hole of the disk. In DVD-R and DVD-RW optical disks, themanagement information is recorded on an NBCA (Narrow Burst CuttingArea). In the DVD-R optical disk, the NBCA is formed within a range offrom 22.71 (+0.06, −0.06) through 23.51 (+0.06, −0.06) [mm], and in theDVD-RW optical disk, the NBCA is formed within a range of from 22.7(+0.05, −0.05) through 23.5 (+0.05, −0.05) [mm].

[0006] The management information is recorded using the RZ modulation,and a playback signal RF (see FIGS. 1(B)-1(E)) obtained with trackingservo control deactivated is binarized and played back.

[0007] The above-mentioned BCA and NBCA ares are pre-pit areas in theDVD-ROM and DVD-RAM optical disks where embossed pits are formedbeforehand. In these optical disks, a variation in signal level due topits (the variation in the signal level having a short period as shownin FIG. 1(C)) is superimposed on the playback signal RF (BCA) (see FIGS.1(B) and 1(C)) obtained when the management information is played back.In contrast, in the DVD-R and DVD-RW optical disks having no pits in theconcerned area thereof, no similar variations are observed in theplayback signal RF (NBCA) (see FIGS. 1(D) and 1(E)) when the managementinformation is obtained. Referring to FIGS. 1(C) and 1(E), T1 is 3±1.5[μsec], and T2 is 8.89n±2 [μsec], where n is 1, 2, 3 or 4.

[0008] The optical disk apparatus that records data to and/or plays backdata from a variety of these optical disks must reliably play back datafrom any of these optical disks.

[0009] The playback signal RF obtained from the BCA and NBCA where themanagement information is recorded has features different from disk typeto disk type and from disk to disk. Specifically, the playback signalobtained from the BCA and NBCA varies in the degree of modulation fromdisk to disk. When the optical disk is decentered, the modulation by thesurface of a mirror changes (a variation in the signal level having alarge period as shown in FIGS. 1(B) and 1(D)).

[0010] In these optical disks, it is difficult to set an appropriatebinarization threshold value when the playback signal obtained from theBCA and NBCA is binarized. Consequently, a reliable playback of themanagement information from a variety of these optical disks isdifficult.

DISCLOSURE OF THE INVENTION

[0011] The present invention has been developed in view of the aboveproblems, and it is an object of the present invention to provide anoptical disk apparatus and a recording method and/or a playback methodof an optical disk, wherein management information recorded in abar-code form is reliably played back from a variety of optical disks.

[0012] To resolve the above mentioned problem, the present invention isapplied to an optical disk apparatus and includes envelope detectormeans which detects an envelope signal of a playback signal, offsetmeans which generates a binarization threshold signal by offsetting theenvelope signal by an offset voltage, bandwidth limiter means whichlimits a high-frequency signal level variation of the playback signal,and binarizing means which binarizes an output signal of the bandwidthlimiter means according to the binarization threshold signal as areference to generate a binary signal.

[0013] Since the optical disk apparatus of the present inventionincludes the envelope detector means which detects the envelope signalof the playback signal, the offset means which generates a binarizationthreshold signal by offsetting the envelope signal by the offsetvoltage, the bandwidth limiter means which limits a high-frequencysignal level variation of the playback signal, and the binarizing meanswhich binarizes the output signal of the bandwidth limiter meansaccording to the binarization threshold signal as a reference togenerate the binary signal, the signal level of the binarizationthreshold signal is appropriately set and the playback signal isbinarized even when the playback signal is varied in the signal levelfrom optical disk type to optical disk type and from optical disk tooptical disk. The management information recorded in a bar-code form isreliably played back from any of a variety of optical disks.

[0014] The present invention is applied to a method for recording dataon an optical disk and/or playing back data recorded on the optical diskand includes the steps of detecting an envelope signal, generating abinarization threshold signal by offsetting the envelope signal by anoffset voltage, and binarizing the playback signal according to thebinarization threshold signal as a reference to generate a binarysignal, subsequent to limiting a high-frequency signal level variationof the playback signal.

[0015] The present invention thus provides the method for recording dataon the optical disk and/or playing back data recorded on the opticaldisk wherein the management information recorded in a bar-code form isreliably played back from any of a variety of optical disks.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a diagram illustrating management information.

[0017]FIG. 2 is a block diagram illustrating an optical disk apparatusof a first embodiment of the present invention.

[0018]FIG. 3 is a signal waveform diagram illustrating the operation ofthe optical disk of FIG. 2.

[0019]FIG. 4 is a signal waveform diagram illustrating the operation inwhich data is recorded on and/or played back from an NBCA in comparisonwith the waveform diagram of FIG. 3.

[0020]FIG. 5 is a block diagram illustrating a demodulator applied to anoptical disk apparatus of a second embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0021] The embodiments of the present invention will now be discussedwith reference to the drawings.

(1) Construction of First Embodiment

[0022]FIG. 2 is a block diagram illustrating an optical disk apparatusof a first embodiment of the present invention. The optical diskapparatus 1 records data to and/or plays back data from an optical disk2 of DVD-ROM, DVD-RAM, DVD-R, DVD-RW type or other type.

[0023] In the optical disk apparatus 1, a spindle motor 3 driven by amotor driver 4 rotates the optical disk 2 at a predetermined rotationalspeed. A predetermined thread mechanism supports and moves an opticalpickup 5 in a radial direction of the optical disk 2. The optical pickup5 directs a laser beam to the optical disk 2, while receiving, at apredetermined photosensor, returning light of the laser beam. Theoptical pickup 5 outputs a signal responsive to the returning light toan RF amplifier 6. The optical pickup 5 under the control of an unshowndriver circuit intermittently raises the amount of light of the laserbeam directed to the optical disk 2. A row of pits is thus formed on therecordable optical disk 2 to record data on the optical disk 2.

[0024] The RF amplifier 6 current-to-voltage converts the signal outputfrom the optical pickup 5 and processes the converted signal, therebygenerating a playback signal RF which varies in signal level inaccordance with a reflectance at a location of the optical disk 2 wherethe laser beam is directed, a tracking error signal which varies insignal level in accordance with a tracking error, and a focus errorsignal which varies in signal level in accordance with a focus error.

[0025] The motor driver 4 is controlled by a system controller 7 whichfunctions in response to a clock that is obtained by processing theplayback signal RF output from the RF amplifier 6. The motor driver 4drives the spindle motor 3. Spindle control is thus performed in theoptical disk apparatus 1. An optical pickup driver 8 is controlled bythe system controller 7 which functions in response to the trackingerror signal and the focus error signal. The optical pickup driver 8moves an objective lens and causes the optical pickup 5 to perform aseek operation. Tracking control and focus control are thus performed inthe optical disk apparatus 1. When the optical pickup 5 performs theseek operation, the laser beam is directed to the BCA, NBCA, etc.

[0026] A signal processor 9 plays back the clock from the playbacksignal RF, and processes the playback signal RF in accordance with theclock, thereby playing back data recorded in the optical disk 2.

[0027] The system controller 7, namely, a computer which controls thegeneral operation of the optical disk apparatus 1, drives the motordriver 4, the optical pickup driver 8, etc. in response to the trackingerror signal, the focus error signal, and a request from a hostapparatus. When the optical disk 2 is loaded or when the power is thenon in the optical disk apparatus 1, information required for datarecording and/or data playback on the optical disk 2 is acquired fromthe optical disk 2. Based on the acquired information, the systemcontroller 7 generally controls the optical disk apparatus 1 so thatdata is recorded to and/or played back from the optical disk 2 inresponse to a request from the host apparatus.

[0028] In these process steps, the system controller 7 determineswhether the BCA or the NBCA is arranged on the optical disk 2 based onthe information acquired from the optical disk 2 at the moment of poweron. If it is determined that the BCA or the NBCA is arranged on theoptical disk 2, the system controller 7 drives the motor driver 4, theoptical pickup driver 8, etc. so that the BCA or the NBCA is sought.With the optical pickup 5 positioned at the BCA or the NBCA subsequentto the seek operation, a binary signal S1 output from a demodulator 10is decoded. The management information recorded at the BCA or the NBCAis then played back.

[0029] When the management information recorded at the BCA or the NBCAis played back, the system controller 7 stores the managementinformation in an internal memory. In accordance with the managementbased on the management information, and the information acquired at thestartup and required for data recording and/or data playback, the systemcontroller 7 controls the general operation of the optical disk 2 fordata recording and/or data playback.

[0030] The demodulator 10 binarizes the playback signal RF with respectto a binarization threshold, thereby outputting the binary signal Si.Specifically, a low-pass filter (LPF) 13 in the demodulator 10 limitsthe bandwidth of the playback signal RF, thereby detecting andoutputting an envelope signal S2 which varies in signal level inaccordance with the envelope of the playback signal RF.

[0031] If the optical disk 2 is of a DVD-ROM or DVD-RAM type in theoptical disk apparatus 1, the BCA is set in a pre-pit area havingembossed pits. Referring to FIGS. 3(A) and 3(B), the playback signal RF(BCA) obtained from the BCA varies in signal level in accordance withthe management information recorded in the BCA. In contrast to thissignal variation, a variation having a short period responsive to thepits formed in the optical disk 2 is observed. Also observed is avariation in signal level having a long period due to a decenteredoptical disk 2. With a cut-off frequency set therewithin, the low-passfilter 13 extracts a signal variation having a long period, therebyoutputting the envelope signal S2 (see FIG. 3(E)).

[0032] If the optical disk 2 is of a DVD-R or DVD-RW type, no pits arearranged in the NBCA. Referring to FIGS. 4(A) and 4(B), the playbacksignal RF (NBCA) obtained from the NBCA has a signal waveform of theplayback signal RF (BCA) having no signal variation having the shortperiod due to the pits. The low-pass filter 13 extracts the signalhaving the level varying with the long period, thereby outputting theenvelope signal S2 (see FIG. 4(E)).

[0033] If the rotational speed of the optical disk 2 is set to 20 [Hz],a cut-off frequency of 20 [kHz] is set in the low-pass filter 13. Theplayback signal RF (BCA) obtained from the BCA becomes the envelopesignal S2 having the long signal variation having the long period as aresult of removing the signal level variation having the short perioddue to the pits. As the playback signal RF (BCA) obtained from the BCA,the playback signal RF (NBCA) from the NBCA also becomes the envelopesignal S2.

[0034] An offset generator 14 generates and outputs an offset voltageV1, which is a predetermined DC voltage. A substracter 16 subtracts theoffset voltage V1 from the envelope signal S2, thereby outputting abinarization threshold signal S3 (see FIGS. 3(E) and 4(E)). Thedemodulator 10 thus generates the binarization threshold signal S3,which serves as a reference for binarizing the playback signal RF, basedon the envelope of the playback signal RF.

[0035] A low-pass filter (LPF) 15 has a cut-off frequency which limitsonly a variation having a short period contained in the playback signalRF (BCA) obtained from the BCA. The low-pass filter 15 thus outputs theplayback signal RF output from the RF amplifier 6 with the bandwidththereof limited. When the playback signal RF (BCA) obtained from the BCAis processed, the low-pass filter 15 suppresses a signal level variationhaving the short period due to the pits and provides an output signal S4which varies in signal level in response to a record in a bar-code formin the BCA, and has a signal level variation having a long period (seeFIGS. 3(C) and 3(D)). When the playback signal RF (NBCA) obtained fromthe NBCA is processed, there is no signal variation arising from thepits in the playback signal RF (NBCA), and the output signal S4 with thesignal level thereof varying in response to the record in the bar-codeform in the NBCA and having the long period is output (see FIGS. 4(C)and 4(D)).

[0036] Specifically, when the rotational speed of the optical disk 2 isset to 20 [Hz], a cut-off frequency of 400 [kHz] is set in the low-passfilter 15.

[0037] A comparator 17 outputs the binary signal S1 of the playbacksignal RF by recognizing the output signal S4 of the low-pass filter 15according to the binarization threshold signal S3.

(2) Operation of the First Embodiment

[0038] When the optical disk apparatus 1 detects the loading of theoptical disk 2, or when the power is on, the optical pickup 5 under thecontrol of the system controller 7 seeks an inner track of the opticaldisk 2, and then plays back the information required to record data toand/or play back data from the optical disk 2. If the informationindicates that the BCA or the NBCA is formed in the optical disk 2, thesystem controller 7 causes the optical pickup 5 to seek these areas.

[0039] When the optical pickup 5 is positioned at the BCA or the NBCA inthe optical disk apparatus 1, the optical pickup 5 receives returninglight reflected from the optical disk 2 to which the optical pickup 5directs a laser beam, with the tracking control of the optical pickupdriver 8 suspended. The RF amplifier 6 processes the signalcorresponding to the returning light, thereby detecting the playbacksignal RF (see FIGS. 3(A) and 3(B), and FIGS. 4(A) and 4(B)) whichvaries in signal level in response to the reflectance of a laser beamfocused position on the optical disk 2. The playback signal RF is inputto the low-pass filter 13 in the demodulator 10. The low-pass filter 13extracts the envelope signal S2, namely, the signal component having thesignal level varying with the long period of the playback signal RF (seeFIGS. 3(E) and 4(E)). The substracter 16 offsets the envelope signal S2by the offset voltage V1, hereby generating the binarization thresholdsignal S3 as a reference signal for binarizing the playback signal RF.

[0040] The low-pass filter 15 suppresses the signal level variation ofthe playback signal RF having the short period due to the pits (seeFIGS. 3(C) and 3(D), and FIGS. 4(C) and (D)). The output signal S4 ofthe low-pass filter 15 is determined according to the binarizationthreshold signal S3, thereby becoming the binary signal S1. The systemcontroller 7 in the optical disk apparatus 1 decodes the binary signalS1, thereby playing back the management signal.

[0041] The optical disk apparatus 1 generates the binarization thresholdsignal S3 for binarizing the playback signal RF based on the envelope ofthe playback signal RF. Even if a decentered optical disk varies theplayback signal RF in signal level with a long period, the playbacksignal RF is binarized with respect to a reference responsive to thesignal level. Even if the degree of modulation becomes different fromdisk to disk with the amplitude of the playback signal RF changingsubstantially, the playback signal RF is binarized using the referencevalue responsive to the change. The optical disk apparatus 1 reliablyplays back the management information recorded in the bar-code form on avariety of optical disks.

[0042] According to the results of experiments, the playback signal RFis reliably binarized if the playback signal RF output from the RFamplifier 6 has an amplitude of 1 [V] even when the signal level of theplayback signal RF varies because of variations in gain of the RFamplifier 6 and variations in the amount of light of the laser beam.

(3) Advantages of the First Embodiment

[0043] The binarization threshold is generated by offsetting theenvelope of the playback signal, and the playback signal is binarizedusing the binarization threshold. The management information recorded inthe bar-code form on a variety of optical disks is reliably played back.

[0044] The envelope of the playback signal is detected using thelow-pass filter. This simple arrangement allows the managementinformation to be reliably detected.

[0045] The offset generator 14 as the offset voltage generator meansgenerates the offset voltage V1. The substracter 16 subtracts the offsetvoltage V1 from the envelope signal, thereby generating the binarizationthreshold. With the offset voltage V1 set and switched as necessary, thebinarization threshold is maintained at an appropriate signal level, andthe management information is thus reliably played back.

(4) Second Embodiment

[0046]FIG. 5 is a block diagram illustrating a demodulator that isincorporated in the optical disk of a second embodiment of the presentinvention. The optical disk apparatus of the second embodiment isidentical in construction to the optical disk apparatus 1 of the firstembodiment except that the demodulator 20 is used instead of thedemodulator 10.

[0047] Rather than using the offset generator 14 and the substracter 16,the demodulator 20 uses a diode 21 to offset the envelope signal S2 bythe forward voltage drop thereof, thereby generating the binarizationthreshold signal S3.

[0048] In the arrangement shown in FIG. 5, the diode adds the forwardvoltage drop as the offset voltage to the envelop signal, therebygenerating the binarization threshold signal. This arrangement simplerin construction than that of the first embodiment still provides thesame advantage as that of the first embodiment.

(5) Alternate Embodiments

[0049] The low-pass filter forms the envelope detector means in each ofthe above embodiments. The present invention is not limited to thisarrangement. The envelope detector means may be any of a variety ofarrangements. For example, the envelope detector means may be fabricatedof a peak-hold circuit, or an envelope detector circuit.

[0050] In the above embodiments, data is recorded to and/or played backfrom the optical disks in compliance with so-called DVD standards. Thepresent invention is not limited to this arrangement. The presentinvention is widely applied to the case in which data is recorded toand/or played back from an optical disk which has the managementinformation recorded in the bar-code form.

[0051] In accordance with the present invention, the offset is added tothe envelope of the playback signal, and the binarization threshold isgenerated. The playback signal is binarized using the binarizationthreshold. The management information recorded in the bar-code form isreliably played back from any of a variety of optical disks.

INDUSTRIAL APPLICABILITY

[0052] The present invention relates to an optical disk apparatus and arecording method and/or a playback method of an optical disk, and isapplied to an optical disk apparatus that records data to and/or playsback data from an optical disk complied with the DVD standards.

1. An optical disk apparatus which records data to and/or plays backdata recorded on an optical disk by directing a laser beam to theoptical disk, comprising: playback signal generator means which receivesreturning light of the laser beam and generates a playback signal whichvaries in signal level in accordance with the reflectance at a locationof the optical disk where the laser beam is directed, envelope detectormeans which detects an envelope signal of the playback signal, offsetmeans which generates a binarization threshold signal by offsetting theenvelope signal by an offset voltage, bandwidth limiter means whichlimits a high-frequency signal level variation of the playback signal,binarizing means which binarizes an output signal of the bandwidthlimiter means according to the binarization threshold signal as areference to generate a binary signal, and decoder means which decodesthe binary signal to demodulate management information recorded in abar-code form on the optical disk.
 2. An optical disk apparatusaccording to claim 1, wherein the envelope detector means is a low-passfilter.
 3. An optical disk apparatus according to claim 1, wherein theoffset means comprises an offset voltage generator for generating theoffset voltage, and a subtracter circuit for offsetting the envelopesignal by the offset voltage.
 4. An optical disk apparatus according toclaim 1, wherein the offset means comprises a diode and wherein theenvelope signal is offset by the offset voltage which is a forwardvoltage drop of the diode.
 5. An optical disk apparatus according toclaim 1, wherein management information in a bar-code form is recordedon an inner track of the optical disk.
 6. An optical disk apparatuswhich records data to and/or plays back data recorded on an optical diskby directing a laser beam to the optical disk, comprising: a lightsource that directs the laser beam to a region which is arranged on aninner track of the optical disk and on which management information isrecorded in a bar-code form, playback signal generator means whichreceives returning light of the laser beam and generates a playbacksignal which varies in signal level in accordance with the reflectanceat a location of the optical disk where the laser beam is directed,envelope detector means which detects an envelope signal of the playbacksignal, offset means which generates a binarization threshold signal byoffsetting the envelope signal by an offset voltage, bandwidth limitermeans which limits a high-frequency signal level variation of theplayback signal, binarizing means which binarizes an output signal ofthe bandwidth limiter means according to the binarization thresholdsignal as a reference to generate a binary signal, and decoder meanswhich decodes the binary signal to demodulate management informationrecorded in a bar-code form on the optical disk.
 7. An optical diskapparatus according to claim 6, wherein the envelope detector means is alow-pass filter.
 8. An optical disk apparatus according to claim 6,wherein the offset means comprises an offset voltage generator forgenerating the offset voltage, and a subtracter circuit for offsettingthe envelope signal by the offset voltage.
 9. An optical disk apparatusaccording to claim 6, wherein the offset means comprises a diode andwherein the envelope signal is offset by the offset voltage which is aforward voltage drop of the diode.
 10. A method for recording data on anoptical disk and/or playing back data recorded on the optical disk bydirecting a laser beam to the optical disk, comprising the steps of:directing the laser beam to a region which is arranged on an inner trackof the optical disk and on which management information is recorded in abar-code form, detecting an envelope signal from a playback signal whichvaries in signal level in accordance with the reflectance at a locationof the optical disk where the laser beam is directed, when returninglight of the laser beam is received, generating a binarization thresholdsignal by offsetting the envelope signal by an offset voltage,binarizing the playback signal according to the binarization thresholdsignal as a reference to generate a binary signal, subsequent tolimiting a high-frequency signal level variation of the playback signal,decoding the binary signal to demodulate the management informationrecorded in a bar-code form on the optical disk, and recording data onthe optical disk and/or playing back data from the optical diskreferencing the demodulated management data.